Is it possible to beat the main story of GTA V using only non-lethal weapons and tactics?

Is it possible to beat the main story of GTA V with never having the character you are currently playing as kill someone?

No, it's not possible.

Sorry about that.

There are missions in the main story where there is no alternative to killing people. Listing them all would be futile, but an example as Michael in the By the Book mission.

No, it's not possible. Some missions that include the death of a person is:

• Prologue - killing security guard
• Carbine Rifles
• Hotel Assassination
• Fresh Meat
• Lamar Down

These are just to name a few. Everything mission at least has to have someone killed. In others there are alternatives.